Delay condenser safety device



June 28, 1960 H. F. DUNLAP DELAY CONDENSER SAFETY DEVICE Filed March 19, 1943 AMPLIFIER TERMINALS F162.

FIG.I.

SE T'BACK SWITCH m E tqm w I? SET-BACK SWITCH mma. m

H IM H H T FIG].

WHEN USING INVENTOR OL M u F mm 7m X M7 H I 2,942,549 DELAY CONDENSER SAFETY DEVICE Filed Mar. 19, 1943,Ser.No.'479,79 7 '2 Claims. cl. 1oz-70.2

This invention relates 'to detonating circuits for explosive projectiles and has particular reference to a novel safety-delay detonating circuit in which premature detonation of the projectile is prevented by. reason of the inclusion in the circuit of a condenser for firing the detonator. The new detonating circuit may be used for. various purposes but is particularly adapted for use with radio proximity fuzes of the type disclosed in'a copending application of M. A. 'Iuve et 211., Serial No. 471,388, filed January 6, 1943. Accordingly, for illustrative purposes, the invention will be described and illustrated in'the form of a detonating circuit suitable for such use.

One object of the invention is to provide a novel safetydelay detonating circuit having a condenser which is charged slowly through a high resistance, whereby a current sufiiciently powerful to fire an electrical squib can be produced by the condenser discharge only when the condenser is charged at least a predetermined amount. A

Unite States circuit made in accordance with the invention comprises a thyratron which may be triggered by any suitable control means, such as aradio proximity fuse, and a plate battery for the thyratron. The squib is connected between the battery and the plate of the thyratron, and a firing condenser is connected in parallel with the battery between the battery and the squib. The condenser is charged by the battery through a high resistance in series with the condenser and the battery, the condenser being operable to fire the squib upon triggering of the thyratron. Accordingly, if the thyratron should be triggered prematurely, the condenser is found at such time to be not sufficiently charged to fire the squib, with the result that the danger of premature detonation is eliminated.

Another object of the invention is to provide a novel safety-delay detonating circuit characterized by its simplicity of arrangement and which is safe and reliable in operation.

These and other objects of the invention may be better understood by reference to the accompanying drawing, in which Fig. 1 is a schematic view of one form of the new detonating circuit;

Fig. 2 is a view similar to Fig. 1 showing a modification of the circuit;

Fig. 3 is a longitudinal sectional view of the housing for the circuit parts;

Fig. 4, 5 and 6 are perspective views of parts of the housing, and

Fig. 7 is a chart illustrating the operation of the circuit.

Referring to Fig. 1 of the drawing, the circuit there shown comprises an electrically operable squib 10 for detonating the usual booster (not shown) of a projectile to explode the main charge therein. The squib is connected to a thyratron 11 having a grid 12, a cathode 13 and a plate 14, one side of the squib being connected directly to the plate. The opposite side of the squib is con- 2,942,549 r I Patented June .23,

projectile from a gun. The switch 16: may be ofany desired form, such as that disclosed in an'application of Bleakney et al., Serial No. 438,506, filed April 10, 1942, and is connected through a high resistance 17 to the positive side of aB battery 18, the negative side of which is connected through another setback switch 19 and'a-conductor 20 to the thyratron cathode 13,.- A firing condenser 22 is connected in parallel with the battery '18 between the resistor 17 and the squib 10 and with the setback switches 16 and '19 in series with the condenser and the battery. The condenser is shunted by a resis'tor 23 for preventing charging of the condenser due'toleakage across the setback switches.

The thyratron 11 is adapted to be triggered by any suitable control means, and to thisend' it is preferred to connect the grid 12 to the output terminal 24 of an amplifier in a radio proximity fuze (not shown) such as that disclosed in the above-identified application of M. A. Tuve et a]. The cathode 13 may be energized by a suitable current source 25.

The circuit shown in Fig. 2 is generally similar to that illustrated in Fig. 1, except that the setback switch 16 is disposed between the positive side of the B battery and the high resistance 17, and the resistor 23 for shunting the firing condenser is connected at one end' between resistance 17 and the setback switch 16 and at the other end to the negative side of the condenser.

The condenser and other elements of the detonating circuit may be arranged in a cylindrical housing 27 mounted in the projectile, the housing being preferably made of an insulating material, such asLucite. The housing, as shown, comprises a main body 28 having a recess 28a in its rear face for receiving the condenser, the resistances, etc., and a cover 29 secured to the body over the recess by rivets 30. In the front face of the main body 28 is a socket 31 for receiving a locator plug (not shown) on the amplifier unit of the fuze, and the cover 29 has a locator plug 32 designed to fit into a socket (not shown) in the rear section of the fuze, which may contain the squib 10. The electrical connections to the elements in the recess 28a may be made through socket terminals 33 in the main body 28 and through plug terminals 34 on the cover 29. The values of the electrical elements shown in Figs. 1 and 2 may vary. For example, the resistor 17 may be 400,000 ohms, the condenser 22 may be .8 micro-farads, and the resistor 23may be 10 megohms.

In the operation of the detonating circuit, the setback switches 16 and 19 close when the projectile is fired from the gun, with the result that the condenser 22 becomes.

charged from B battery 18 through the high resistance 17. After the condenser has been charged at least a pre determined amount, it is operable to explode the squib l0 electrically when the thyratron 11 is triggered from the amplifier terminal 24. In the event that the thyratron should break or be accidentally triggered before condenser 22 is sufiiciently charged, the squib 10 cannot be fired. It will be noted that if the high resistance 17 should be accidentally short-circuited, the squib 10 cannot be fired as long as the thyratron 11 does not conduct prematurely, since the condenser charging current from battery 18 does not flow through the squib in the normal condition of the thyratron. For the circuit to detonate prematurely, it is necessary for the high resistance 17 to be short-circuited during a time that the thyratron '11 conducts prematurely. Each of these accidental events should be relatively rare individually, and thesimultanected to a setback switch 16 which is normally open but neous ocurrence of both should be practically impossible.

In the use of the new circuit, it has been found that if the condenser 22 is .5 micro-farads, upon receipt 'of the appropriate impulse from the amplifier, the squib 10 will 3 not firebefore' the voltage has risen to .76 of its 'final value, and, will always fire afterthe voltagehas reached. .96 of its final value. Between these two values, firing of the squib 10 is erratic. If a condenser 22 of .6 micro farads isused, the squibz llltwiilf not fire; before,- the voltage haSIiSQHLtO 68 of its final: value'an'd willalways the after the voltage has reached .9l. of'its final value, the firing of-the squib being erratic between these two values. The

values given, abovejwere, obtained with a battery 18- having'a maximum voltage, of 97 volts and a minimum voltageof 90 volts, the mostunfavorable of these voltages being used in determining each of the limits given above. Referring to the chart of Fig; 7, the abscissas represent the time of firing of the squib by the condenser, and? the ordinates representthe percentage ot'the, final voltage to which: thecondenser may be charged. If the; condenser 22 is .6 micro-farads and is charged through 417,000 ohms, making RC on the chart equal to one-fourth second, then, squib 10 wil1 be safe for at least one-fourth second and will always be ready tov fire, before the lapseof three-fourths of a second after the condenser, starts to charge. The uncertain region is well within the interval RC-3RC'. If the, condenser 22 is .5, microrfarads and the I resistance 17 is one-half a megohm (againmaking the RC constant equal to one-fourth second), .thesquib 10 will be, safe, for, at least one-fourth second, and. will always beready to fire within a one second interval after the condenser starts to charge, the uncertain region being Well within the interval RC-4RC. e

What is claimed is: 1

1'. A safety-delay .detonating system, comprising a thyratron having a plate, a grid and a cathode, a plate battery, an electrical detonator, a high-resistance resistor,

' two setback-operated switches, conductors connecting the thyratron plate through the detonator, one of the switches and the resistor to the positive. terminal of the battery, conductors connecting the thyratron cathode to the negative terminal of the battery through the other switch, and a firing condenser connected to the two switch terminals remote from the battery,whereby no voltage can be. applied to the condenser before both switches are. closed,

2. A safety-delay detonating system as defined in claim 1, wherein a resistor ispermanently connected across the terminals of the condenser to. prevent accidental'charging. of said condenser by leakage across the switches.

References Cited in the file of-this patent UNITED STATES. PATENTS 

